Best Way To Hook MTS30 Up To 388

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I have no idea what any of this means but the selector is pointing at the 5 on this dial; and I have the red lead in the top socket and the black in the bottom (following instructions in the manual). I'm probably doing it wrong, but I can't tell which side is DC and tha manual isn't helping
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I have no idea what any of this means but the selector is pointing at the 5 on this dial; and I have the red lead in the top socket and the black in the bottom (following instructions in the manual). I'm probably doing it wrong, but I can't tell which side is DC and tha manual isn't helping
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If you have the red probe in the top socket and the mode select dial is pointing to the “5”, you’re measuring current. And you want to measure for AC volts, not DC. Did you read the section in the manual? It’s section 1-5-4 on page 1-23 of the Maintenance section of the manual:


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You want to measure for AC volts. Plug the red probe into the middle socket, black in the bottom, and set your dial to the “200” like this:

1E41F496-8B91-4661-BE16-095CFBFC6AB2.webp


There are two sets of test points on each of the 4 amp cards…TP2 and TPG. I’ve circled the two sets on one of the amp cards here:

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You need to measure for AC volts at all 8 sets of test points while all 8 tracks are record enabled and the transport is in REC PLAY.
 
Yes, that's much clearer thanks. and the results are... Terrible

Zeroes all the way :(
 
Looking at the specs for your meter I actually think it’s not capable of measuring the bias voltage. The voltage should be around 150mV, the smallest amount your meter can read is 100mV, but the bigger issue is the frequency. Meters vary in how accurate they are in measuring AC volts at different frequency ranges. Your meter doesn’t even give a specification for its accuracy at any frequency and bias signal is a very high frequency…100kHz on the 388. So if you want to know for sure I think you’re going to have to get a different meter or borrow a different one that’s capable of measuring with some accuracy in a 100kHz mV range. Sorry.
 
I didn't adjust any of the trimpots. Should I have?
No. Remember, we’re not adjusting the bias levels, we’re just trying to see if there is any bias signal at all. Your meter is telling you there’s none, but I’m telling you I don’t think your meter is capable of measuring the bias signal.
 
I don't think I could afford a meter that is capable of doing that. It sounds like it'd be way over £50
 
I don't think I could afford a meter that is capable of doing that. It sounds like it'd be way over £50
It would be something used if you’re on a budget, and yeah probably more than that. So that’s the thing with this stuff, you either have to have the correct tools to maintain and repair or know somebody who does. I don’t know how to help further if the necessary tools aren’t available.
 
You could find the cheapest unit capable of doing the job here and post the link below
 
That’s really similar to what you have already. And it doesn’t give any specs on the usable frequency range.

I’m really hesitant to spend time shopping when you already gave a budget that will not buy anything new that will do the job and then you want me to find something new that will do the job. But new it’s going to be 5-10x your budget. And we do t even know for sure if we’re on the right track with what the issue is. I think your best bet is to take it to a tech.
 
I doubt I'd find anyone within a hundred miles who even knows how to fix stuff like this now.

The closest person I can think of lives in the Scottish Isles.
 
Assuming there is any bias (which I doubt) what would the next step be and could it be done in a weekend by me?

If so I could probably hire a suitable device. If anyone knows what that might be. I don't really have any use for a multimeter on a regular basis.

Also, why has it lost bias?
 
Assuming there is any bias (which I doubt) what would the next step be and could it be done in a weekend by me?

We do not know whether your bias signal system is working or not. We don’t really know anything right now. As a result, there is no way to know what the next step is, or how long it would take to resolve, both because we don’t know what the cause or causes of your current problem are, and I don’t have a clear picture of your abilities.

If so I could probably hire a suitable device. If anyone knows what that might be.

Again, any AC voltmeter that can measure millivolt range signal at a frequency of 100kHz or better will do.

Also, why has it lost bias?

?

If we knew that, we would know what to do to solve the problem. We don’t know anything at this point.
 
It seems I'm in a double bind. If I can't afford the £300+ multitmeters you'd recommend then I certainly can't afford to send it off to someone else to fix. Even if I could get a suitable multimeter for less used you've made me so unsure about my choices that I'd have no idea which to buy.

I might as well just give up.
 
It seems I'm in a double bind. If I can't afford the £300+ multitmeters you'd recommend then I certainly can't afford to send it off to someone else to fix. Even if I could get a suitable multimeter for less used you've made me so unsure about my choices that I'd have no idea which to buy.

I might as well just give up.
It’s unfortunate you feel I’m responsible for your current situation, but for whatever reason we always seem to come to some negative end when I try to help you. This is exclusively unique to you. I always hope it will go better, but it just never does.

You are able to look at the specifications for any meter new or used for which you can find a manual online. You can do the same thing I’d be doing if I was doing this work for you. I’ve given you all the information you need. Find a meter for sale. Find the manual. Look in the specifications. It’ll say the AC volts accuracy for a given frequency range. If it doesn’t list accuracy up to or beyond 100kHz then it’s not rated to measure AC volts in that range, and won’t give you accurate results. We’re not too concerned about accuracy. We ARE concerned about a meter’s ability to measure 100kHz AC volts at all. If a meter’s specs show some accuracy for AC volts above the audio band (like greater than 20kHz), it might pick something up at 100kHz. I don’t know. But if it doesn’t list accuracy specs specific to frequency range at all, I doubt it will, and if it doesn’t list accuracy specs at all it’s not worth trying. So, you do not have to do what I would do. You don’t have to listen to me at all. You are getting free advice. It’s worth…free. If it was me the first thing I would do is see if the bias amp is doing anything. I’d use my Fluke 85 DMM. I believe the 83 and 87 series would work too. You can find these used. My meter isn’t accurate at 100kHz necessarily, but it’ll measure something up there. For accuracy I’d use my scope. Again, you don’t have to do what I would do, but I’m not there, can’t see your machine, you typically offer very little detail in your posts so I don’t want to dive deep and be off-track. We’ve discussed this before. I think you want me to spend hours looking through manuals and specs and tell you what to get. I’m resistant to do that because I don’t have that kind of time, you can do it yourself, and I’m a little wary about giving you advice because, as noted above, we somehow end up in some zone of negativity where you’re upset with me for the advice I’ve offered, even though you either don’t follow the advice or debate with me about points that are not relevant.

So…

Here we are again. I hope this is of some help. I’m not confident it is.
 
Yes…it will measure frequency up to 220MHz with that degree of accuracy.

We don’t need to measure the frequency of your bias oscillator.

We need to measure if your bias system is outputting voltage. I can’t find a manual for that meter to see if it measures AC volts at at least 100kHz. That datasheet doesn’t specify. I suppose if it can measure frequency to 220MHz then maybe it can measure AC volts to 100kHz? But we’re talking apples and oranges a bit here.

I love how you totally blew past everything I said in my last post. I’ve made you so unsure about your choices but you keep posting stuff I assume for me to look at. I’m not sure it’s a good idea for you to follow my advice or for me to continue offering it. I’m open to any advice the rest of the community has here but I’m not sure it’s in any of our best interests for me to continue responding. Maybe others will chime in. I don’t know.
 
I can't find any mention of frequency in relation to AC on any of the data sheets for handheld multimeters I've looked at starting in the £800 range and working my way down.
 
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